A continued investigation of detailed metabolism of vitamins A and D will continue with special emphasis on isolation and identification of new metabolites. Studies on the molecular basis for the regulation of 1,25-(OH) 2D3 synthesis by parathyroid hormone and plasma inorganic phosphorus will be emphasized as will the enzymology of 25-OH-D3-1-hydroxylase and vitamin D3-25-hydroxylase. The role of vitamin D metabolites in phosphate metabolism will be examined. Isolation and characterization of the rat liver microsomal prothrombin precursr will continue. The calcium binding prosthetic group has been chemically cleaved from prothrombin and effects to characterize it will continue. the in vitro microsomal system which converts rat liver precursor of prothrombin will be further characterized. Purification and characterization of the low molecular weight Se-containing moiety of glutathione peroxidase will be pursued. The relation of glutathione peroxidase to Se-deficiency defects and to dietary vitamin E, sulfur-containing amino acids, and unsaturated lipids will receive attention and will include studies on the eye lens. The mechanisms of antagonism of Ag and tri-ortho-cresyl phosphate and Se and vitamin E functions will be studied as will the relation of vitamin E to the liver mixed function oxidase system and to free-radical damage induced by CC14.